Activation of local aldosterone system within podocytes is involved in apoptosis under diabetic conditions

Abstract

Previous studies have shown that mineralocorticoid receptor (MCR) blocker reduces proteinuria in diabetic nephropathy (DN), but the role of aldosterone in podocyte injury has never been explored in DN. This study was undertaken to elucidate whether a local aldosterone system existed in podocytes and to examine its role in podocyte apoptosis under diabetic conditions. In vitro, immortalized podocytes were exposed to 5.6 mM glucose (NG), NG + 24.4 mM mannitol, and 30 mM glucose (HG) with or without 10(-7) M spironolactone (SPR). In vivo, 32 Sprague-Dawley rats were injected with diluent (C, n = 16) or streptozotocin intraperitoneally [diabetes mellitus (DM), n = 16], and 8 rats from each group were treated with SPR for 3 mo. Aldosterone synthase (CYP11B2) and MCR mRNA and protein expression were determined by real-time PCR and Western blot, respectively, and aldosterone levels by radioimmunoassay. Western blot for apoptosis-related molecules, Hoechst 33342 staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to determine apoptosis. CYP11B2 and MCR expression were significantly higher in HG-stimulated podocytes and DM glomeruli compared with NG cells and C glomeruli, respectively, along with increased aldosterone levels. Western blot analysis revealed that cleaved caspase-3 and Bax expression was significantly increased, whereas Bcl-2 expression was significantly decreased in HG-stimulated podocytes and in DM glomeruli. Apoptosis determined by Hoechst 33342 staining and TUNEL assay were also significantly increased in podocytes under diabetic conditions. These changes in the expression of apoptosis-related proteins and the increase in apoptotic cells were inhibited by SPR treatment. These findings suggest that a local aldosterone system is activated and is involved in podocyte apoptosis under diabetic conditions.

Myeloid Mineralocorticoid Receptor Activation Contributes to Progressive Kidney Disease

“…24 Furthermore, systemic MR blockade reduces podocyte loss or damage in diabetic rats. 11,12 Therefore, our data showing a lack of prevention of albuminuria in diseased mice with systemic MR blockade or podocyte MR deficiency indicates that podocyte damage in this rapidly progressive GN model is mediated by injury mechanisms that are independent of MR. However, the ability of MR antagonists to reduce proteinuria in CKD, suggests that podocyte MR signaling may play a role in chronic proteinuria.…”

“…Recent in vitro studies have suggested that MR signaling can induce apoptosis in podocytes and oxidative stress in macrophages, 12,13 which supports a role for MR signaling in these cell types in kidney disease. In addition, an MR deficiency in myeloid cells protects against cardiovascular injury and ischemic cerebral infarcts by reducing inflammation and fibrosis.…”

Hypothalamic-pituitary-adrenal axis activity is associated with the prevalence of chronic kidney disease in diabetic patients

“…When F-DST was above the cut-off value of 1.8 μg/dL, we consecutively measured diurnal variation of cortisol and ACTH, and cortisol and ACTH after corticotrophin-releasing hormone (CRH) test, as reported previously [25,26]. Furthermore, patients with basal ACTH levels lower than 10 pg/mL underwent abdominal computed tomogmainly by aldosterone and has an important role in the development of renal disease, including CKD, in humans [9][10][11][12]. MR stimulation causes progression of renal diseases by inducing glomerular podocyte injury or mesangial cell proliferation as well as by mediating blood pressure changes due to renal Na + reabsorption [9,10].…”

New insights into the renoprotective actions of the renin inhibitor aliskiren in experimental renal disease

“…29 Podocytes also produce Ang II 25,26,28 and aldosterone. 30 Angiotensin type 1 receptors are expressed on mesangial cells 19,24,31 and podocytes 26,28,32 and mineralocorticoid receptors are also expressed by both cell types. 29,33,34 The likely importance of the local glomerular RAAS relates to the pathogenesis of glomeruloscleorsis and the loss of glomerular permselectivity observed in many glomerular diseases.…”

“…44 Aldosterone can also damage podocytes by inducing apoptosis and reducing nephrin gene expression. 30,33,45 Thus, through autocrine or endocrine mechanisms, Ang II and aldosterone may induce damage and/or pro-fibrotic pathways in mesangial cells or podocytes, and thus contribute to glomerular damage.…”